Glaciological processes associated with the terminal overdeepening at Svínafellsjökull

Overdeepenings (topographic closed-depressions in glacier beds) influence subglacial drainage system transmissivity and the continuity of sediment transfer through glacial systems, thus affecting subglacial water pressure and basal sediment layer thickness, and thereby modulating rates of subglacial erosion and patterns of landscape evolution (Hooke, 1991; Alley et al., 2003; Cook and Swift, 2012). Efficient evacuation of erosion products is essential to maintain subglacial bedrock erosion, and theoretical and empirical work indicates that the adverse slopes of overdeepenings restrict efficient transfer of basal sediment (Hooke, 1991; Alley et al., 1998; Creyts and Clarke, 2010), leading to the stabilisation of overdeepened glacier bed profiles (Alley et al. 2003; Patton et al. 2016). Terminal overdeepenings, and overdeepened beds generally, are very common, apparently because of enhanced meltwater availability downglacier of the ELA greatly enhances erosion rates beneath the tongue by increasing rates of basal sliding (Herman et al. 2011) and sediment flushing (Swift et al. 2005). Evidence of the influence of overdeepenings on subglacial drainage and sediment transfer processes is abundant at Svínafellsjökull, though some processes remain controversial or poorly understood, and some evidence challenges the assumptions of the ‘stabilising hypothesis’ advocated by, for example, Alley et al. (2003).